STATIC EXCHANGE AND CLUSTER MODELING OF CORE ELECTRON SHAKEUP SPECTRAOF SURFACE ADSORBATES - CO CU(100)/

An nb initio static exchange approach is devised for calculations of t he core-electron shake phenomenon of large species. The approach emplo ys appropriately spin-coupled two-hole potentials for the various shak eup/ shakeoff channels. It is far extendable in the number of atoms tr eated, in the one-particle basis set, and in the spectral range, while restricted in correlation to full intrachannel correlation. Using clu ster modeling it is implemented for shake spectra of molecules adsorbe d on surfaces. A demonstration is given for the oxygen and carbon shak e spectra of COCuN, N=0,14,50, modeling CO/Cu(100). The reduction of s hake energies and the accompanying increase in intensity are well reco vered by the large cluster employed (COCu50), while the small cluster (COCu14) could only recover half the total shakeup/shakeoff intensity created by the absorption. An assignment of the strong low-lying shake up states could be obtained in terms of orbital excitations and in ter ms of local versus delocalized characters of these excitations. Result s for the oxygen and carbon shakeup spectra of free carbon monoxide ar e analyzed in some detail in view of data from high-resolution experim ents and from other theoretical approaches.